Substrate for semiconductor device and method of manufacturing the same

ABSTRACT

Metal which forms a crystalline insulation layer is sputtered at a target and deposited as a film on a silicon substrate, the metal is chemically combined with reactive gas around the silicon substrate to thereby grow a crystal layer of a crystalline insulation substance, and a voltage is applied to the substrate so that ions of the reactive gas around the substrate are attracted to a surface of the silicon substrate and chemically combined with silicon, whereby an insulation silicon compound layer is formed. As a result, a structure is obtained in which a crystalline insulation layer is formed on a crystalline silicon layer through an amorphous insulation film which is formed by a silicon compound which has an excellent insulation characteristic. Hence, it is possible to epitaxially grow other semiconductor layer or a crystalline ferroelectric layer on a surface of the crystalline insulation layer, which makes it possible to form a three dimensional semiconductor device, a composite semiconductor device, a high performance semiconductor memory device or the like. Thus, it is possible to obtain a semiconductor device which is new and highly integrated at an inexpensive cost.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a substrate for a semiconductordevice, such as an SOI substrate and a substrate for an FET which has anMFS structure (metallic film/ferroelectric film/semiconductor layerstructure), which is suitable for crystal growth of a semiconductorlayer or a fereroelectric layer on a silicon substrate through aninsulation layer, and to a method of manufacturing such a substrate.More particularly, the present invention relates to a substrate for asemiconductor device in which a crystalline insulation layer may begrown through an insulation layer which has an excellent insulationcharacteristic on a silicon substrate for the purpose of growing asemiconducting crystal layer, a ferroelectric crystal layer, etc., andto a method of manufacturing such a substrate.

[0002] In relation to an SOI substrate for growing a semiconductingcrystal layer on an insulation layer, for instance, among known methodsare a method which requires to bond two silicon substrate seating oxidefilms with each other and polish one of the two substrates to therebyleave a thin semiconductor layer. And another method requires to injectoxygen or the like at a surface of a silicon substrate to a constantdepth and to anneal so that an insulation layer is buried in asemiconductor substrate.

[0003] Meanwhile, in a semiconductor memory device using a ferroelectriclayer, the ferroelectric layer is formed on a semiconductor layer or ona surface of an electrode metal such as platinum through an insulationfilm. In an MFS structure in which a ferroelectric layer is formed on asemiconductor layer, an oxide film is formed between the ferroelectriclayer and the semiconductor layer, thereby degrading a crystal qualityor morphology, or an interface state density between the ferroelectriclayer and the semiconductor layer becomes large. Where the ferroelectriclayer is formed on an insulation film, it is not possible to grow aferroelectric layer which has an excellent crystal quality on theinsulation film which is amorphous.

[0004] As described above, during fabrication of a semiconductor device,while it is necessary to epitaxially grow a semiconductor layer or acrystalline ferroelectric layer on a semiconductor substrate through aninsulation layer in some cases, since the insulation layer is amorphous,it is not possible to grow a crystalline layer directly on a surface ofthe insulation layer.

[0005] Further, in the method which requires to polish one of bondedsilicon layers for thinning the one silicon layer, it is extremelydifficult to polish the silicon layer into an uniformly thin layer andpolishing is laborious, and therefore, a quality crystalline surface ishardly obtained. In the method which requires to inject oxygen at asurface layer portion of a semiconductor substrate, on the other hand,ion bombardment greatly degrades a surface of a semiconductor layer, andtherefore, a high quality crystalline surface is hardly obtained,either. As a result, a crystal layer which is formed on such adeteriorated crystalline surface as well has a deteriorated crystalquality.

[0006] On the other hand, the inventors of the present inventioninvented a method of epitaxially growing an YSZ thin film on a siliconsubstrate and presented the method to Shingaku Gihou (ED96-42, CPM96-27,May 1996). This method makes it possible to obtain a crystallineinsulation layer on a silicon substrate and epitaxially grow asemiconductor layer or a ferroelectric layer on a surface of the YSZ.However, since an YSZ thin film which is formed on a silicon substrateis a crystalline metallic oxide film and hence migrates ions, electricinsulation of the YSZ thin film is inferior to that of a silicon oxidefilm or a silicon nitride film, and therefore, the YSZ thin filmslightly degrades electric characteristics.

SUMMARY OF THE INVENTION

[0007] The present invention has been made to solve such problems.Accordingly, an object of the present invention is to provide asubstrate for a semiconductor device which is suitable to grow a crystallayer, such as a semiconductor layer and a ferroelectric layer, on othersemiconductor layer through an insulation layer during fabrication of asemiconductor device and which sufficiently improves electric insulationagainst a silicon substrate which serves as a base.

[0008] Other object of the present invention is to provide a method offorming a crystalline insulation layer on a semiconductor layer throughan insulation silicon compound.

[0009] A substrate for a semiconductor device according to the presentinvention comprises a crytalline silicon substrate, an insulationsilicon compound layer which is formed on the silicon substrate, and acrystalline insulation layer which is epitaxially grown on theinsulation silicon compound layer.

[0010] As herein termed, a “substrate for a semiconductor device” refersto a base for growing crystalline semiconductor layers and ferroelectriclayers one atop the other, but not a complete base for a semiconductordevice. In this context, a “substrate for a semiconductor device” coversa structure that an insulation silicon compound layer or a ferroelectriclayer is formed in a portion of a semiconductor device, or on a stackedsemiconductor layer, etc.

[0011] Where the crystalline insulation layer is formed by at least onespecies which is selected from a group of YSZ (yttria stabilizedzirconia), Al₂O₃ (sapphire), CeO₂ (ceria), MgO (magnesia) and ZrO₂(zirconia) and the insulation silicon compound layer is formed by atleast one of silicon oxide, silicon nitride and silicon nitride oxide, asubstrate for a semiconductor device which is particularly excellent ininsulation and crystalline characteristics is obtained.

[0012] A method of manufacturing a substrate for a semiconductor deviceaccording to the present invention is comprising the steps of:

[0013] growing a crystalline insulation layer on a silicon substrate bysputtering a metal which forms said crystalline insulation layer from atarget, and chemically combining with reactive gas around said siliconsubstrate; and

[0014] forming an insulation silicon compound layer by applying avoltage to said silicon substrate so that ions of said reactive gasaround said substrate are attracted to a surface of said siliconsubstrate and chemically combined with silicon.

[0015] More specifically, the silicon substrate and the target aredisposed facing each other within a reactive sputtering apparatus, thereactive gas is supplied into the apparatus in such a manner that thereis a larger amount of the reactive gas around the substrate than aroundthe target, and inert gas which is supplied into the apparatus isdischarged and the crystal layer of the crystalline insulation substanceis grown, whereby the substrate for a semiconductor device is obtained.Even more specifically, the target may be a composite target or an alloytarget of zirconium (Zr) and yttrium (Y), the reactive gas may beoxygen, the crystalline insulation layer may be YSZ, and the crystallineinsulation substance may be silicon oxide.

[0016] When Ce, Al, Mg or Zr is used as the target, it is possible togrow CeO₂, Al₂O₃, MgO or ZrO₂, respectively, as the crystallineinsulation layer.

[0017] The reactive gas may be supplied into the sputtering apparatuswith the target covered with a cover which has an opening at a portionof the target which is faced with the silicon substrate. This simplestructure allows to deposit the layer as it is in the metal mode on thesubstrate without chemically combining the target and to epitaxiallygrow a compound of the metal of the target and the reactive gas on thesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a cross sectional explanatory diagram showing a stackedstructure of a substrate for a semiconductor device according to thepresent invention;

[0019]FIG. 2 is a schematic diagram showing an example of a sputteringapparatus for obtaining the stacked structure according to the presentinvention; and

[0020]FIG. 3 is a view showing an example of a target which is used inthe apparatus which is shown in FIG. 2.

DETAILED DESCRIPTION

[0021] As shown in FIG. 1, in a substrate for a semiconductor deviceaccording to the present invention, an insulation silicon compound layer2 which has an excellent electric insulation characteristic, such as asilicon oxide film, is formed between a silicon substrate 1 and acrystalline insulation layer 3, such as YSZ, which is epitaxially grownon the silicon substrate 1.

[0022] The silicon substrate 1 is formed by a silicon monocrystallinelayer. With respect to the conductivity of the silicon substrate 1, thesilicon substrate 1 may be an n type layer, a p type layer, asemiconductor circuit in which an n type region, a p type region and thelike are formed, or a silicon semiconductor layer is formed entirely orpartially on other semiconductor layer or the like.

[0023] As the crystalline insulation layer (monocrystalline insulationlayer) 3, metallic compound, for example, YSZ, Al₂O₃, CeO₂, MgO, ZrO₂ orany other metal oxide, which allows a crystalline structure to growthereon is used. A crystalline structure of a metallic compound isobtained by growing metal on the silicon substrate 1 while oxidized,fluorinated, nitrided or otherwise chemically combined with metal on thesubstrate 1. The thickness of the crystalline insulation layer 3 isdifferent depending on an application. Used as a ground for growingother semiconductor layer or a crystalline ferroelectric layer, thecrystalline insulation layer 3 is normally about 5 to 20 nm which isthick enough as such a ground. Depending on an application, thecrystalline insulation layer 3 may be formed into a thickness ofapproximately 0.5 to 1 μm.

[0024] As the insulation silicon compound layer 2, silicon oxide such asSiO₂, silicon nitride such as Si₃N₄, silicon nitride oxide such as SiON,or the like is used. As described later, such a compound is obtained bychemically combination of oxygen, nitrogen or the like which passesthrough the crystalline insulation layer 3 and silicon, during growth ofthe crystalline insulation layer 3, and therefore, is limited to acompound which is obtained by chemical combination with a substancewhich passes through the crystalline insulation layer 3. Whiledetermined in accordance with a breakdown voltage, etc., which isrequired in an expected application, the thickness of the insulationsilicon compound layer 2 is normally about 10 to 60 nm.

[0025] In the substrate for a semiconductor device according to thepresent invention, the monocrystalline insulation layer is formed on thesilicon substrate through the amorphous insulation film. Hence, asurface of the semiconductor substrate has a crystalline structure,which allows to epitaxially grow a further semiconductor layer or acrystalline ferroelectric layer on the surface of the semiconductorsubstrate. In addition, since the amorphous insulation film which isformed by a silicon compound is formed between the monocrystallineinsulation layer and the crystalline silicon layer, the semiconductorsubstrate has an excellent insulation characteristic. This achieves verystrong electric insulation between a layer which is formed at thesurface of the crystalline insulation layer and the silicon substratewhich is formed beneath. In short, while the monocrystalline insulationlayer is a metallic compound, such as metal oxide, as described earlier,and therefore, has a slightly inferior insulation characteristic due topossible ion migration, silicon oxide, silicon nitride or the likerealizes excellent electric characteristics. This allows to obtain anSOI substrate, to repeatedly form semiconductor layers throughinsulation layers on the crystalline silicon layer in which asemiconductor circuit is formed such that a three dimensional circuit isformed, or to form a crystalline ferroelectric layer of a ferroelectricmaterial or the like into a quality crystalline structure to therebyobtain a semiconductor memory device which has excellentcharacteristics.

[0026] Now, a method of manufacturing the substrate for a semiconductordevice according to the present invention will be described in relationto a specific example in which YSZ crystals are grown on a siliconsubstrate through a silicon oxide film. FIG. 2 is a schematic diagram ofa reactive sputtering apparatus for epitaxial growth, showing an exampleof an apparatus which is used in the manufacturing method.

[0027] First, a substrate 1 of a silicon semiconducting crystal layerwhich has a diameter of 1 inch is mounted to a substrate seater(mounting plate) 12 within a vacuum chamber 11 of the sputteringapparatus, and a target 4 is fixed to a target holder 13 which isdisposed so as to face the substrate seater 12. The target 4 is acomposite target which is obtained by attaching about six yttrium (Y)plates 42 whose each side A is about 10 mm and thickness is about 1 mmto a Zr plate 41 whose diameter D is about 100 mm and thickness is about5 mm in a circumferential direction, for example as shown in FIG. 3, oran alloy target which is obtained by adding Y to Zr at 8 to 10%. Aroundthe target 4, a cover 14 which has an opening 14 a which has a diameterof about 20 mm or a collimator which has an equivalent effect isdisposed in front of the target 4. Metal to be sputtered is passedthrough the opening 14 a, while avoiding exposure of the target 4 tooxygen and resulting oxidation of the target 4. An electrode pole 15 isdisposed in contact with the target holder 13, and a first power source16 is connected between the electrode pole 15 and an earth with theelectrode pole 15 serving as the negative pole so that a plasmadischarge is created within the vacuum chamber 11. A gas introducingpipe 17 is disposed to one wall of the vacuum chamber 11 for supplyingAr and O₂ to the vacuum chamber 11, while a gas discharging exit 18 isformed in other wall of the vacuum chamber 11. Further, in thisapparatus, a second power source 19 for attracting oxygen ions towardthe substrate 1 and anodizating is provided between the substrate seater12 and the earth with the substrate seater 12 serving as the positivepole. Denoted at 20 is a solenoid coil for developing a magnetic fieldat a surface of the target, and denoted at 21 is a solenoid coil forpressing the magnetic field against the surface of the target.

[0028] In such an apparatus, the silicon substrate 1 was mounted to thesubstrate seater 12 and in such a manner that a distance from the target4 was 72 mm, for instance. As gas to introduce, Ar gas was supplied at aconstant gas pressure of 10 mTorr, for example, and with a flow rate tooxygen of O₂ /(Ar+O₂)=5.8%, for instance. While epitaxially growing YSZat a discharge power of 80 W and a substrate temperature of 600 to 800°C., a positive voltage of approximately 50 V was applied from the secondpower source 19 to the substrate for anodization. As a result, an YSZcrystal layer was epitaxially grown at a rate of 40 nm/min and an SiO₂layer was formed at a rate of about 1 nm/min between the substrate andthe YSZ crystal layer. As to a relationship between the YSZ crystallayer and the SiO₂ layer in terms of thickness, the lower the appliedvoltage from the second power source 19 is, the thinner the SiO₂ layeris so that the proportion of the SiO₂ layer is small. Conversely, thehigher the voltage from the second power source 19 is, the larger theproportion of the SiO₂ layer is. Further, the higher the discharge power(which is the voltage from the first power source 16) is, the thickerthe YSZ crystal layer is and the larger the proportion of the YSZcrystal layer is. Conversely, the lower the discharge power is, thesmaller the proportion of the YSZ crystal layer is. With respect to thedischarge power, an applied voltage may be varied in the range of about300 to 500 V. Meanwhile, the voltage for anodization (i.e., the voltagefrom the second power source 19) may be varied in the range of about 20to 100 V. Hence, it is possible to grow each layer into a desiredthickness.

[0029] As described above, the manufacturing method according to thepresent invention provide to sputter the metal which forms thecrystalline insulation layer and grow the metallic compound on thesubstrate while reacting the metal with the reactive gas which is aroundthe substrate and consequently forming the crystalline insulation layerof oxide or the like, and at the same time to create an insulationsilicon compound on the surface of the substrate. That is, as describedearlier, the inventors of the present invention disclosed, in ShingakuGihou ED96-42, a method in which a layer is grown as it is in the metalmode without oxidizing the target and oxidized while grown, so that anYSZ thin film is epitaxially grown on a silicon substrate at a highdeposition speed. Utilizing the nature of a crystalline insulation layersuch as an YSZ thin film that the crystalline insulation layer transmitsoxygen ions and the like, the present invention requires to apply avoltage to a silicon substrate to thereby attract ions such as oxygenions to the silicon substrate and chemically combine the ions withsilicon while epitaxially growing a crystalline insulation layer such asan YSZ thin film, so that an insulation film (insulation siliconcompound layer) which is formed by a silicon compound such as SiO₂ whichhas an excellent electric insulation characteristic is formed betweenthe crystalline insulation layer such as YSZ and the crystalline siliconlayer. In this case, the insulation film such as SiO₂ may be formed at adifferent time from growth of the crystalline insulation layer. So itproduces a substrate for a semiconductor device which is formed by thecrystalline silicon substrate, the insulation silicon compound layerwhich is formed on the silicon substrate, and the crystalline insulationlayer which is formed on the insulation silicon compound layer.

[0030] In the manufacturing method according to the present invention,since the crystalline insulation layer is grown as it is in the metalmode which prohibits the target from chemically combining with theatmosphere, it is easy to epitaxially grow an insulation layer which hasan excellent crystal structure. Further, to form the insulation film ofa silicon compound on the silicon surface under the condition in whichthe crystalline insulation layer is provided on the silicon substrate,an amorphous insulation film may be formed at the interface between thecrystalline insulation layer and the silicon substrate, withoutdegrading the crystal quality of the crystalline insulation layer. Inaddition, as it is possible to form the crystalline insulation layer andthe silicon compound approximately at the same time, it is possible toform the substrate for a semiconductor device in a short period of time.

[0031] While the target 4 is covered with the cover 14 which has theopening 14 a in the sputtering apparatus described above, this isbecause if the target 4 is oxidized due to oxygen of the reactive gas,the oxide is sputtered and the sputtered oxide prevents to grow a filmin the metal mode, and prohibited crystal growth eventually creates anamorphous film. Therefore, as far as oxidation of the target 4 isavoided, such a cover 14 is not necessary. In other words, in theexample described above, the metal is sputtered and grown epitaxially tothe surface of the substrate, and at the same time, utilizing activationof the metal, the metal is oxidized by oxygen of the atmosphere so thatcrystals of the metal oxide grows. Hence, the cover 14 may be omitted sothat the partial pressure of the reactive gas, such as the partialpressure of oxygen, at the target 4 becomes very low, and the reactivegas such as oxygen may be blown toward the substrate 1 so that thepartial pressure of the reactive gas becomes high only at the substrate1.

[0032] Although the YSZ crystal layer is grown using Zr and Y as thetarget in the example described above, a film may be grown in the metalmode with a low partial pressure of oxygen in a similar manner using Ceas the target and oxidized at the surface of the substrate to therebygrow a crystal layer of CeO₂. Further, it is possible to grow a crystallayer of Al₂O₃ in a similar manner when Al is used as the target, and itis possible to grow a crystal layer of MgO or ZrO₂ when Mg or Zr is usedas the target. In addition, instead of using oxygen as the atmosphere atthe surface of the substrate, fluorine or nitrogen may be blown towardthe substrate, so that a crystalline insulation layer which is formed bya compound of metal and fluorine or nitrogen is obtained.

[0033] Further, while the example described above requires that oxygenions are attracted toward the silicon substrate, and silicon is oxidizedso that silicon oxide is created between the crystalline insulationlayer and the silicon substrate, nitrogen ions may be attracted andchemically combined to create silicon nitride. Alternatively, bothoxygen ions and nitrogen ions may be attracted to create a siliconnitride oxide layer.

[0034] Further, although the crystalline insulation layer is grown bysputtering in the example described above, it is possible to manufacturein a similar manner in other method such as laser absorption, reactiveevaporation, etc, if the chemical combination at the target isprohibitted, and chemical combination may be caused during growth to thesurface of the substrate.

[0035] According to the present invention, it is possible to obtain astructure in which a crystalline insulation layer is formed on acrystalline silicon layer through an amorphous insulation film which isformed by a silicon compound which has an excellent insulationcharacteristic. Hence, it is possible to epitaxially grow othersemiconductor layer or a crystalline ferroelectric layer on a surface ofthe crystalline insulation layer, which makes it possible to form athree dimensional semiconductor device, a composite semiconductordevice, a high performance semiconductor memory device or the like.Thus, it is possible to obtain a semiconductor device which is new andhighly integrated at an inexpensive cost.

[0036] Although preferred embodiments have been described in somedetail, it is to be understood that certain changes can be made by thoseskilled in the art without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A substrate for a semiconductor device,comprising: a crytalline silicon substrate; an insulation siliconcompound layer which is formed on said silicon substrate; and acrystalline insulation layer which is epitaxially grown on saidinsulation silicon compound layer.
 2. The substrate of claim 1 , whereinsaid crystalline insulation layer is formed by at least one specieswhich is selected from a group of YSZ, Al₂O₃, CeO₂, MgO and ZrO₂.
 3. Thesubstrate of claim 1 , wherein said insulation silicon compound layer isformed by at least one of silicon oxide, silicon nitride and siliconnitride oxide.
 4. A method of manufacturing a semiconductor substratefor a semiconductor device comprising the steps of: growing acrystalline insulation layer on a silicon substrate by sputtering ametal which forms said crystalline insulation layer from a target, andchemically combining with reactive gas around said silicon substrate;and forming an insulation silicon compound layer by applying a voltageto said silicon substrate so that ions of said reactive gas around saidsubstrate are attracted to a surface of said silicon substrate andchemically combined with silicon.
 5. The method of claim 4 , whereinsaid silicon substrate and said target are disposed facing each otherwithin a reactive sputtering apparatus, said reactive gas is suppliedinto said apparatus in such a manner that there is a larger amount ofsaid reactive gas around said substrate than around said target, andinert gas which is supplied into said apparatus is discharged, wherebysaid crystal layer of said crystalline insulation substance is grown. 6.The method of claim 5 , wherein said target is a composite target or analloy target of zirconium and yttrium, said reactive gas is oxygen, saidcrystalline insulation layer is YSZ, and said insulation siliconcompound layer is silicon oxide.
 7. The method of claim 5 , wherein Ceis used as said target, and a crystal layer of CeO₂ is grown as saidcrystalline insulation layer.
 8. The method of claim 5 , wherein Al isused as said-target, and a crystal layer of Al₂O₃ is grown as saidcrystalline insulation layer.
 9. The method of claim 5 , wherein Mg isused as said target, and a crystal layer of MgO is grown as saidcrystalline insulation layer.
 10. The method of claim 5 , wherein Zr isused as said target, and a crystal layer of ZrO₂ is grown as saidcrystalline insulation layer.
 11. The method of claim 4 , wherein saidreactive gas is supplied into said sputtering apparatus, with saidtarget covered with a cover which has an opening at a portion of saidtarget which is faced with said silicon substrate.